Microemulsion composition to increase injectivity of water produced in reservoirs

ABSTRACT

The present invention addresses to an oil-in-water microemulsion composition to increase the injectivity of produced water in reservoirs of oil production fields, contemplates a solution that has the potential to reduce the water-oil interfacial tension, to increase the mobility of produced water in the reservoir and to restore the wettability of the reservoir rock.

FIELD OF THE INVENTION

The present invention addresses to a microemulsion composition that canbe used as a washer cushion applied in all oil producing fields aimingat increasing injectivity in face of the injection of produced water.

DESCRIPTION OF THE STATE OF THE ART

The injection of water into reservoirs is a technique used to increaseoil recovery. It is the most widely used secondary recovery method inthe world. In general, seawater is collected and submitted to membranefiltration processes to remove solids and sulfates. The quality of thiswater meets the requirements for injectivity in reservoirs.

The injection of water in reservoirs, a well-known process in the stateof the art, may have low efficiency when the injected water is producedwater, which contains oil, solids and chemicals in its composition,leading to the loss of injectivity. With the addition of surfactantproducts, in the form of a microemulsion, the injectivity is improved asa result of the reduction of the interfacial tension and the alterationof the wettability of the porous medium.

Recently, the possibility of injecting produced water into thereservoirs was evaluated as an alternative to the disposal of this waterat sea, especially on platforms where the quality of the produced watersdoes not meet the current legislation in terms of oil and grease content(OGC). However, the initial tests of injection of produced water haveshown significant reductions in the injectivity index of the wells,after the incorporation of the produced water in the injected fluid,compromising the operation and production of these platforms.

Currently, the acidic treatment is the treatment considered inreinjection designs to restore the injectivity of wells. This treatmentis carried out from stimulation boats due to the necessary volume. Inthis operation, acids such as HCl and/or HF are pumped into thereservoir in volumes of about 50 bbl/m² (5,962 m³/m²) of open area tothe flow, in order to remove the damage caused at the well-reservoirinterface. With the increase in water reinjection demand from 2021onwards, stimulation boats may become a critical resource to meet thefrequency required for the treatment of all wells subjected to producedwater reinjection. In addition, the wells have limitations regarding thenumber of acidic treatments due to problems associated with thecorrosion process and the great wear of the strings of the platformsthat will be subjected to reinjection.

In this way, finding alternative, low-cost solutions, with lessaggressiveness to metallic lines and with the possibility of treatmentfrom the platform to restore/mitigate the loss of injectivity of thewells can have a significant impact on reinjection designs.

Some characteristics of microemulsions, such as spontaneous formation,clear appearance, thermodynamic stability and low viscosity, made thesesystems attractive and convenient for many applications. The widespreaduse and interest in microemulsions are mainly based on the highsolubilization capacity of hydrophilic and hydrophobic compounds such asoil and salts, their large interfacial area and ultra-low interfacialtension.

A microemulsion is defined as a visually transparent dispersion ofdroplets of one liquid dispersed in a second immiscible liquid andstabilized by an interfacial film of surfactant molecules. Generally, inaddition to the surfactant itself, the interfacial film is made up of aco-surfactant, such as an intermediate chain alcohol or an amine. Thedroplet diameter of a microemulsion is on the order of 10 to 100 nm andits formation is independent of the mixing order of its components, butrequires high concentration of surfactant, low interfacial tension andan adequate hydrophilic-lipophilic balance (HLB).

Microemulsions and macroemulsions, the latter known in the state of theart as emulsions, are similar simply because they are formed by amixture of water, oil and surfactant. However, it is important to notethat microemulsions are thermodynamically stable and formedspontaneously, while emulsions are not thermodynamically stable, and areonly formed if subjected to a stirring procedure (mechanical energy).Furthermore, microemulsions are transparent and emulsions are opaque.

An oil-in-water microemulsion is similar to the normal micelle, wherethe hydrophilic part of the surfactant is oriented towards thecontinuous water phase and the non-polar part is oriented towards theinterior of the micelle. The presence of the co-surfactant with thesurfactant in the microemulsion provides flexibility to the interface,in addition to reducing the interfacial tension, directing the curvatureof the interface to an energetically more favorable dispersion, thusdecreasing the interfacial viscosity. As a consequence, thesolubilization capacity of a microemulsion is generally much greaterthan that of micellar solubilization. The microemulsion enhances theadvantages of the aqueous solution of surfactant and the pure organicsolvent.

Ultra-low interfacial tension and high solubilization capacity are twodesirable characteristics in microemulsion systems.

For its preparation, low energy is required, because its formation isspontaneous and its characteristics can be controlled by temperature andsalinity. All these characteristics make microemulsions also haveapplications in improved oil recovery, in the extraction of organiccompounds, in chemical synthesis, in the preparation of nanoparticlesand further in the solubilization of toxic compounds in order to protectthe environment.

Document PI0605007-7 discloses a composition for remediation of soilsand solid residues contaminated by high molecular weight hydrocarbons,by means of a microemulsion formed by a surfactant/co-surfactantmixture, an organic compound and an aqueous phase, sufficient tocomplete 100% by volume. Said microemulsion comprises a co-surfactant,which can be butanol, and a surfactant, which can be formed by one ormore substances that can be chosen between a lauryl alcohol ethoxylate(LAE) and an oleyl alcohol ethoxylated (OAE); and an organic chemicalcompound, which can be formed by one or more substances that can bechosen from decane, toluene, cyclohexane, terpene, and orange oil.

Document PI0802390-5 describes a microemulsion composition thatcomprises a mixture of a combination of surfactants and co-surfactants,an oil phase, and an aqueous phase; and a method for advanced recoveryof heavy oil comprising the steps of injecting a bank containing saidmicroemulsion composition, injecting a bank of a polymeric solution andinjecting water. This microemulsion composition can be applied insandstone and carbonate reservoirs, containing oils with values lowerthan 22.30° API, in onshore and offshore fields.

SHAW, D. “Introduction to Colloid and Surface Chemistry”, 4th ed., 1996,Oxford Butterworth/Heinemann Publishing Ltd describes that the dropdiameter of a microemulsion is on the order of 10 to 100 nm and itsformation is independent of the order of mixing of its components, butrequires a high concentration of surfactant and an adequatehydrophilic-lipophilic balance (HLB). The presence of alcohol as aco-surfactant has the function of decreasing the interfacial viscosity,destabilizing the lamellar crystalline structures, increasing theinterfacial area and inducing changes in the curvature of the interface.Phase equilibrium transitions can occur due to variations in salinity,temperature, concentration and type of surfactants and co-surfactantspresent in the composition.

In the study by ZHOU, M., RHUE, R. (2000), “Screening commercialsurfactants suitable for remediation DNAPL source zones bysolubilization”, Environment Science Technology, v. 34, pp. 1985-1990,demonstrated that the oil solubilization potential is inverselyproportional to the square root of the interfacial tension. Therefore,the solubilization ratio (volume of the organic phase solubilized in themicroemulsion divided by the volume of surfactant used) increases as theinterfacial tension is reduced.

PERKINS, T. K.; GONZALEZ, J. A. (1985) “The effect of thermoelasticstresses on injection well fracturing”, Society of Petroleum EngineersJournal, v. 25, pp. 78-88, developed a numerical method to calculateinduced thermoelastic stresses within regions of thin elliptical shape.It is evident that this theory can be applied to calculate fracturelengths, downhole pressures (BHPs) and elliptical shapes of the floodfront as the injection process progresses.

However, the use of microemulsion to increase the injectivity of waterproduced in reservoirs has not yet been used. In this way, in order tosolve such problems, the present invention was developed by means of amicroemulsion composition called a washer cushion with the ability tosolubilize the oil present in the water, disperse suspended solids andrestore the wettability of the reservoirs, favoring the removal ofdamage at the reservoir-well interface and increasing the injectivityindex of wells subjected to the reinjection of produced water. Theability to remove oil associated with the low pH of some formulations iscapable of removing corrosion products, and the reduction of water-oilinterfacial tension makes this composition very efficient in restoringpermeability. In addition, the washer cushion is a product that hasgreater efficiency for removing damage caused in this scenario ofreinjection of water produced in laboratory tests compared to otherproducts, including commercial ones.

The present invention has as technical advantages the ability to reducethe water-oil interfacial tension and solubilize the oil dispersed inthe produced water, reduce capillary pressure, increase the fluidmobility in the reservoir and, consequently, remove/attenuate the damageto injection wells caused in the scenario of injection of producedwater.

From an economic point of view, the continuous injection at lowconcentration in the water, as well as the injection of the cushiondirectly from the platform, promote significant advantages, since theyuse smaller volumes of fluids, compared to the acidification process,and further avoid the use of boats that have high daily rental costs. Inaddition, the washer cushion must be less aggressive in terms ofcorrosiveness than conventional acidic treatment.

BRIEF DESCRIPTION OF THE INVENTION

The present invention addresses to an oil-in-water microemulsioncomposition that can be used as a concentrated washer cushion toincrease the injectivity of produced water in reservoirs subjected tothe reinjection of produced water.

The composition can vary according to the properties of the producedwater (chemical composition, salinity, pH) and of the reservoir(composition of the formation water and temperature). This treatmentalternative is very important from a strategic point of view for theproduction of oil and gas, having a positive impact from anenvironmental point of view.

The present invention applies to all producing fields aiming atincreasing injectivity in face of the injection of produced water.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be described in more detail below, withreference to the attached figures which, in a schematic form and notlimiting the inventive scope, represent examples of its embodiment. Inthe drawings, there are:

FIG. 1 illustrating an evaluation of compatibility at 60° C. of theformulations with saline water in mixing ratios 30/70 and 70/30;

FIG. 2 illustrating a compatibility test between commercial product andsaline water in mixing ratios 10/90, 30/70, 50/50 and 70/30;

FIG. 3 illustrating a graph of permeability and flow rate as a functionof injected porous volume from a laboratory test with injection ofacidic microemulsion cushion;

FIG. 4 illustrating a graph of permeability and flow rate as a functionof injected porous volume from a laboratory test with injection ofhydrochloric acid cushion pH=2.4;

FIG. 5 illustrating a graph of permeability versus accumulated volumeinjected after a cushion of acidic microemulsion in tests with plug onplatform;

FIG. 6 illustrating a graph of permeability versus accumulated volumeinjected after a diesel cushion in tests with plug on platform;

FIG. 7 illustrating a graph of permeability versus accumulated volumeinjected after a kerosene cushion in tests with plug on platform;

FIG. 8 illustrating a curve (Q/P)/(Q₀/P₀) during the injection ofproduced water with continuous dosing of 100 mg/l of the microemulsionin tests with plug on platform compared to the curve of (Q/P)/(Q₀/P₀)during produced water flow only;

FIG. 9 illustrating the sample interface (a) before the flow of producedwater, (b) after flow of only produced water and (c) flow of producedwater with the addition of 100 mg/L of the microemulsion.

FIG. 10 illustrating the loss of injectivity as a function of theaccumulated volume injected of produced water in a well subjected to thecontinuous injection of microemulsion compared to a previous period inwhich there was no injection of the product;

FIG. 11 illustrating the loss of injectivity as a function of theaccumulated volume of produced water injected into a well on the sameplatform as the well tested in FIG. 10 , but without the injection ofthe microemulsion, used for comparison, eliminating possiblefluctuations in the quality of the produced water and reservoirparameters.

DETAILED DESCRIPTION OF THE INVENTION

The oil-in-water microemulsion composition to increase the injectivityof water produced in reservoirs, object of the present invention,contemplates a solution that has the potential to reduce the water-oilinterfacial tension, increase the mobility of the water produced in thereservoir and restore the wettability of the reservoir rock. Thus, thecomposition comprises the following components:

-   -   a mixture of one or more surfactants/co-surfactants;    -   an organic chemical compound such as the oil phase; and    -   an aqueous phase, sufficient to complete 100% by volume.

The surfactants used can be formed by one or more substances that can bechosen between: a lauryl alcohol ethoxylate (LAE) and a sodium laurylether sulfate (SLES). Said mixture has a percentage by volume inrelation to the total volume of microemulsion comprised in a range ofvalues between 1% and 70%.

The co-surfactants used are low molecular weight alcohols, such asn-butanol, sec-butanol, iso-propanol and isoamyl and compounds of theglycol ether family such as butyl glycol.

The surfactant/co-surfactant mixture can be made in differentproportions according to the desired tolerance to salinity andtemperature of the water produced.

The oil phase can be formed by one or more substances that can be chosenfrom: organic solvents, n-paraffin, kerosene, refined oils and vegetableoils. The nature of the oil phase should be as similar as possible tothe nature of the reservoir fluid.

The oil phase has percentage in volume in relation to the total volumeof microemulsion in a range of values between 1% and 50%. Thecomposition has a clear and transparent appearance, with a variableviscosity according to the concentration of the components.

The interfacial tension between the microemulsion and the oil in thereservoir is on the order of 0.01 dyne/cm (1 μN/cm).

The aqueous phase used includes pure water, saline water, water withneutral pH, acid and alkaline.

The present invention is a promising alternative because it has theability to restore the wettability of the reservoir to water, which isgiven by the balance between the interfacial forces between the solidand the oil, the oil and the water and the water and the solid, favoringthe increase of injectivity of the produced water. The possibility ofwetting a surface depends on the cohesive forces of the fluid and theinteractions between the solid surface and the fluid.

The microemulsion composition can be applied in the form of aconcentrated washer cushion, in a single operation in large volumes, orby continuous dosing at low concentrations in the produced water. Theprocedure will be defined according to each application scenario.

EXAMPLES

For validation of the composition and proof of performance in increasinginjectivity, object of the present invention, tests were carried out inporous media representative of reservoirs and field test with thecontinuous dosing at low concentrations in the produced water.

Example 1: Tests Performed in the Laboratory

The first tests were carried out in the laboratory. In addition to themicroemulsion described herein, tests were carried out with commercialproducts and with pure acid. The samples used in these tests had beensubjected to the flow of water produced on a platform to quantify theloss of injectivity. In these tests, the reservoir rock sample isconnected to the point of interest (e.g., flotator outlet at theproduction plant) and the produced water flow. The parameters monitoredthroughout the test are flow and pressure. With the data obtained andusing the modeling of loss of injectivity described by PERKINS, T. K.;GONZALEZ, J. A. (1985) “The effect of thermoelastic stresses oninjection well fracturing”, Society of Petroleum Engineers Journal, v.25, p. 78-88, it is possible to estimate the injectivity loss in thesample and obtain the water/rock quality parameter.

In the laboratory tests, the samples were initially submitted to theflow of clean water (without solids or oil) to establish the initialpermeability threshold. The composition of this water was similar tothat of the water produced on a platform.

It should be highlighted that the compatibility of the product with theproduced water is fundamental. Thus, in addition to the flow tests inporous medium, compatibility tests were carried out in different mixingproportions, as shown in FIG. 1 . One of the commercial productsevaluated, for example, proved to be incompatible with water, making itsuse unfeasible, as seen in FIG. 2 . After the water flow, 5 porousvolumes of the products of interest were injected. A 24-hour soaking wasperformed and a new flow of clean water were performed. The sameprocedure was used for all products. The evaluation of the test consistsof comparing the permeability before and after the injection/soaking ofthe products. If the permeability is the same, it means that there wasno restoration. If it decreases, the product has caused increased damageto the sample. When an increase in permeability is observed, theapplication of the product can be considered successful. The higher theincrease, the more effective the product. Both the acidic microemulsionand pure hydrochloric acid (HCl) showed an increase in permeabilityafter soaking. However, the performance of the microemulsion was muchhigher, probably due to its ability to also act in the solubilization ofthe oil phase. Acid, on the other hand, will only be effective inremoving solids such as corrosion products.

As can be seen in FIG. 3 , as a result of the test performed with theacid microemulsion, the curves of permeability versus injected porousvolumes are shown. The thin lines indicate the flow rate (1, 10 and 40mL/min). As can be seen, there is a variation in permeability as afunction of injection flow rate. The evaluation of the microemulsionefficiency was performed at a flow rate of 10 mL/min. Prior to productinjection, the permeability was close to 100 mD (0.0986923 μm²). Afterthe injection, the permeability reached 350 mD (0.34542305 μm²).

FIG. 4 shows the same results for the test with hydrochloric acid (0.1mol/L). The pH used was the same in both products: 2.4. There was alsoan increase in permeability, but it was lower than that observed in FIG.3 .

Example 2: Tests Performed on the Platform with Plug Samples

In addition to laboratory tests, tests were performed directly on theplatform with plugs. The procedure was similar to that described above:a flow of produced water from the flotator outlet was carried out in aporous medium, the injection of 5 porous volumes of acidic microemulsionand a new flow of produced water. In the same way as in the laboratorytests, the flow and pressure were monitored. An important difference isthat there was no soaking period, the second flow of produced water wasstarted immediately after the injection of the porous volumes ofmicroemulsion. The idea was to represent a scenario of product injectionvia the platform, during which there will be no closing period. Inaddition to the microemulsion, diesel and kerosene were evaluated. Thetests to evaluate the efficiency of the formulation for the removal ofdamage from the injection of a cushion showed that there was arestoration of about 65% of the permeability of the porous medium afterthe damage caused by the injection of water produced on a platform(comparison between the final value of permeability after the first flowof produced water and the initial value immediately after productinjection), as shown in FIG. 5 . No gain was observed with the use ofdiesel or kerosene (FIGS. 6 and 7 ).

In addition to the cushion injection test, a test was carried outconsidering the continuous injection of the microemulsion, using theproduced water itself as a base. A concentration of 100 ppm of productwas used. While the cushion aims at restoring injectivity, thecontinuous injection aims at reducing the loss caused by the presence ofoil. In this test, the product was mixed with the produced water beforebeing injected into the sample. The flow and pressure were alsomonitored.

To evaluate the efficiency of the formulation for the attenuation ofdamage from the continuous injection of 100 ppm in the produced water,the results showed a less accentuated loss of injectivity, when comparedto the test with the porous medium subjected to the flow of producedwater only (FIGS. 8 and 9 ). In this case, the composition added to theproduced water acts mainly by reducing the damage effect generated bythe oil dispersed in the water.

Example 3: Field Test

On the platform, an injection test was also carried out directly in theinjection well. The continuous injection of the microemulsion wascarried out at concentrations ranging from 100 to 350 ppm. This test wasperformed after the well acidification treatment and compared with theinjectivity behavior of a previous acidification.

The efficiency of the product is evident by the change of slope in thecurve of loss of injectivity of the well in FIG. 10 from the injectionof the microemulsion indicated by the vertical line. The same is notobserved in another well that did not have the continuous injection ofthe microemulsion (FIG. 11 ) and, therefore, it was used for comparison,eliminating possible oscillations in the quality of the produced waterand parameters of the reservoir.

It should be noted that, although the present invention has beendescribed in relation to the attached drawings, it may undergomodifications and adaptations by technicians skilled on the subject,depending on the specific situation, but provided that it is within theinventive scope defined herein.

1- A MICROEMULSION COMPOSITION TO INCREASE INJECTIVITY OF WATER PRODUCED IN RESERVOIRS, characterized in that it comprises: a mixture of one or more surfactants and co-surfactants comprised in a range of values between 1% and 70% by volume, in relation to the total volume of microemulsion; an oil phase comprised in a range of values between 1% and 50% by volume, in relation to the total volume of microemulsion; an aqueous phase to complete 100% by volume. 2- THE COMPOSITION according to claim 1, characterized in that the used surfactants are formed by one or more substances chosen from a lauryl alcohol ethoxylate (LAE) and a sodium lauryl ether sulfate (SLES). 3- THE COMPOSITION according to claim 1, characterized in that the co-surfactants used are low molecular weight alcohols, such as n-butanol, sec-butanol, iso-propanol and isoamyl and compounds of the glycol ether family, such as butyl glycol. 4- THE COMPOSITION according to claim 1, characterized in that the oil phase is formed by one or more substances chosen from organic solvents, n-paraffin, kerosene, refined oils and vegetable oils. 5- THE COMPOSITION according to claim 1, characterized in that the aqueous phase used is pure water, saline water, water with neutral, acidic and alkaline pH. 